Disclosed herein are optical fibers that can be used for the measurement of temperature and strain. More specifically disclosed herein are optical fibers that can be used for an independent measurement of temperature and strain.
Brillouin scattering in an optical fiber is used for distributed strain and temperature measurement as the frequency shift of back scattered Brillouin Stokes (in the fiber) is dependent on both temperature and strain that are applied to the optical fiber during operation. In order to measure temperature or strain independently, the overall frequency shift of the Brillouin scattering peak need to be de-coupled into a temperature-induced shift and a strain-induced shift.
In order to distinguish between the effects of temperature and strain-induced shifts, a few methods have been proposed and applied: 1) using a sensor system where two fibers are deployed with one of the fibers being isolated from the strain; 2) a sensor system that uses at least two fibers or a dual core fiber with different temperature and strain shift coefficients for each fiber or each core; 3) using a few-mode optical fiber; or 4) dispersion-shifted fiber with multiple Brillouin scattering peaks which have different temperature and strain shift coefficients.
All of these methods of distinguishing between temperature and strain-induced shifts suffer from drawbacks.